This invention relates to power supplies and power supply methods and more particularly to systems and methods for producing uninterruptible power.
Uninterruptible Power Supplies (UPS) are widely used to provide power to electronic components in the event that the alternating current (AC) utility input voltage fails. UPSs are now widely used, for example with computers, including but not limited to personal computers, workstations, and mainframe computers, to insure that valuable data is not lost and that the computer can continue to operate notwithstanding temporary loss of the AC utility input voltage. There are a variety of different types of UPSs, including on-line and standby UPSs. Each of these types has its attendant advantages and disadvantages. Consequently, the selection of an appropriate type of UPS for a particular application generally depends on the nature of the application, e.g., the voltage regulation, current capacity, cost and reliability desired.
U.S. Pat. No. 6,122,181 to Oughton, Jr. describes systems and methods for producing standby uninterruptible power for an AC load that rectify an AC utility input voltage to produce a rectified voltage and that activate a DC battery voltage in response to a predetermined change in the AC utility input voltage to thereby produce a standby DC voltage. The rectified voltage and the standby DC voltage are connected to an AC load that is also capable of operating on DC power, such as an AC load that includes input rectification, to thereby produce standby uninterruptible power without the need for potentially costly, bulky, and/or unreliable inverters or converters.
U.S. Pat. No. 6,181,029 to Berglund et al. describes a power system that includes a battery back-up unit (BBU) that provides battery back up support for a plurality of power supplies that include respective input rectifiers in combination with a respective boost stage that provides power factor correction. The outputs of the boost stages are monitored to control application of power to the power supplies by the BBU from an AC source and a battery.
xe2x80x9cNew Power Supply Optimised for New Telecom Networks and Services,xe2x80x9d by Marquet et al., IEEE INTELEC""99 Conference Proceedings (1999), and xe2x80x9cNew Approach to the rAC Powering Architecture for Telecom/Datacom Convergence,xe2x80x9d by Gonzalez et al., IEEE INTELEC 2000 Conference Proceedings (2000), describe power distribution systems in which AC mains voltage is rectified at the input of telecommunications equipment and distributed directly to AC/DC converters, such as centralized AC/DC converters and AC/DC converter modules on boards that include other functional circuitry, e.g., computer power supply boards. When a mains failure occurs, backup is provided by a high voltage battery connecting at the input of the centralized AC/DC converters and/or to the on-board modules. An off-line AC/DC converter may be used to charge the battery. Power factor correction may be implemented in a distributed fashion or may be implemented in the form of a centralized power factor converter placed in parallel with the rectifier.
Although the aforementioned techniques can effectively provide standby power, there is an ongoing need for improved systems and methods for providing reliable power.
According to embodiments of the invention, an uninterruptible power supply (UPS) system includes an AC input port configured to be connected to an AC power source, a DC input port configured to be connected to a DC power source and an output port configured to be connected to an AC load. The system further includes a rectifier circuit coupled to the AC input port, and a power transfer control circuit coupled to the rectifier circuit output, the DC input port and the output port. The power transfer control circuit is operative to produce a DC voltage at the output port from a rectified voltage produced by the rectifier circuit in a first mode of operation and to produce a DC voltage at the output port from a DC voltage at the DC input port in a second mode of operation. The power transfer control circuit includes a current control circuit configured to be coupled between the output port and at least one of the rectifier circuit and the DC input port and operative to control a current from at least one of the rectifier circuit and the DC input port responsive to a control input. The power transfer control circuit also includes a switching circuit operative to couple and decouple the DC input port to and from the output port.
In some embodiments of the invention, the current control circuit is operative to control a power factor and/or harmonic current at the AC input port responsive to the control input. For example, the current control circuit may comprise a power factor correcting boost regulator circuit series-coupled between the rectifier circuit and the output port. The current control circuit may also be operative to regulate a voltage at the output port responsive to the control input.
In other embodiments of the invention, the power transfer control circuit further comprises a DC/DC converter circuit coupled between the DC input port and the output port. The DC/DC converter circuit may be operative to generate a boosted DC voltage at the output port from a DC voltage at the DC input port in the second mode of operation, and may provide galvanic, e.g., transformer, isolation between the DC input port and the output port in the second mode of operation.
In other embodiments of the invention, a UPS system includes an AC input port configured to be connected to an AC power source, a DC input port configured to be connected to a DC power source, and an output port configured to be connected to an AC load. The UPS system further includes a rectifier circuit coupled to the AC input port and a switching circuit operative to couple and decouple the DC port to and from the output port responsive to a first control input. A power factor correction circuit is configured to connect the rectifier circuit to the output port and operative to control a power factor at the input port responsive to a second control input.
In still other embodiments of the invention, a UPS system includes an AC input port configured to be connected to an AC power source, a DC input port configured to be connected to a DC power source and an output port configured to be connected to an AC load. The system further includes a rectifier circuit having an input coupled to the AC input port and an output coupled to the output port. A power transfer control circuit is coupled to the rectifier circuit output, the DC input port and the output port. The power transfer control circuit is operative to produce a DC voltage at the output port from a rectified voltage produced by the rectifier circuit in a first mode of operation and to produce a DC voltage at the output port from a DC voltage at the DC input port in a second mode of operation. The power transfer control circuit includes a DC/DC converter circuit configured to be coupled between the DC input port and the output port, e.g., a combination of a forward converter circuit and a switching circuit operative to couple and decouple the forward converter circuit to and from the output port.
In additional embodiments of the invention, an uninterruptible power supply system includes a plurality of UPS subsystems in a ganged, e.g., parallel-connected, configuration. Each of the UPS subsystems includes an AC input port, a DC input port and an output port. A rectifier circuit is coupled to the AC input port and a power transfer control circuit is coupled to the rectifier circuit output, the DC input port and the output port. The power transfer control circuit is operative to produce a DC voltage at the output port from a rectified voltage produced by the rectifier circuit in a first mode of operation and to produce a DC voltage at the output port from a DC voltage at the DC input port in a second mode of operation. The plurality of UPS subsystems are configured to be connected in common at their output ports to a load including at least one AC load. A power transfer control circuit may include a current control circuit configured to be connected between the output port and at least one of the rectifier circuit and the DC input port and operative to control a current from the at least one of the rectifier circuit and the DC input port responsive to a control input.
In method embodiments of the invention, power is supplied to an AC load by applying an AC voltage to a rectifier circuit to produce a rectified voltage and controlling a current from the rectifier circuit while producing a DC voltage at the AC load from the rectified voltage. A DC power source is then coupled to the AC load to produce a DC voltage at the AC load from the DC power source. The DC power source may be decoupled from the AC load concurrent with the step of controlling a current from the rectifier circuit while producing an AC voltage at the AC load from the rectified voltage.
In other method embodiments of the invention, power is supplied to an AC load by applying an AC voltage to a rectifier circuit to produce a rectified voltage. A DC voltage is applied to a DC IDC converter circuit to produce a converted DC voltage. A DC voltage is produced at the AC load from the rectified voltage, and then a DC voltage is produced at the AC load from the converted DC voltage.
UPS systems and methods according to embodiments of the invention can provide one or more advantages. Using a current control circuit to control power factor can allow a UPS system to correct power factor associated with AC loads, such as low complexity power supplies, that lack integral power factor correction capability. In ganged operation, UPS systems according to embodiments of the invention can provide desirable output voltage and current characteristics that facilitate power sharing. Using a DC/DC converter to provide standby DC power can allow DC power to be obtained from sources that might otherwise be incompatible, such as 48 V positive-grounded telecommunications power supplies.